This invention relates to electrical switching devices and more particularly to switches which include both mechanical contacts and solid state switching devices connected to achieve arcless current interruption.
Certain switching applications such as the control of DC power in an aircraft electrical power system, require the use of DC contactors which are capable of providing arcless current interruption and low power dissipation. Although it is possible to avoid arcing by making DC contactors which utilize solid state switching components, such contactors are considered feasible only at modest current levels, such as less than about 50 amperes. When higher steady state currents are encountered, the power dissipation and heating in the solid state components becomes unacceptable. On the other hand, electromechanical relays offer the advantage of providing high current handling capacity with low power dissipation. Therefore, it is advantageous to combine mechanical contacts and solid state switching elements to achieve arc-less current interruption and low steady state power dissipation.
Critical applications such as aircraft electrical systems also require switching devices which include failure protection capability. This includes the detection of a failed switch component with subsequent disabling of the switching device.